Recently, there are demands for reduction in feature size and for high precision on semiconductor integrated circuit and the fine and high-precision semiconductor integrated circuit has generally been prepared by imprint technology.
The imprint technology is a technology for transcribing a desirable pattern to surface of a substrate by pressing a mold having concavity or convexity which corresponds to a desirable pattern to be formed on the substrate against a coating film which is formed on the surface of substrate. Utilizing this technology, it is possible to form a nano-scale fine pattern. Among the imprint technologies, the technology for forming an ultrafine pattern having size of from several hundreds to several nanometer (nm) is especially referred to as nanoimprint technology.
On the nanoimprint technology, a process for forming pattern is classified roughly into two types depending on type of material used in formation of coating film on surface of substrate. One type is a process for transcribing a pattern to coating film, which comprises steps of heating a coating film formed on surface of a substrate to plasticize, of pressing a mold against the coating film, and of cooling the coating film to solidify. Another type is a process in which at least one of used mold and substrate is made of light-permeable material and a pattern is transcribed by steps of applying a photo-curable composition in the form of liquid to a substrate to form a coating film, of pressing the mold against the coating film, and of irradiating the coating film with light through the mold or the substrate to cure the coating film. Among them, the photo-imprint process in which the pattern is transcribed through light-irradiation has widely been used as the nanoimprint technology, because it is possible to form a high-precision pattern. A development of photo-curable composition which can suitably be used in the photo-imprint process has been advanced.
In the nanoimprint technology, adhesion between surface of substrate and pattern obtained by curing coating film and release property between pattern and mold are important factors. In relation to release property, several techniques such as a process comprising a step of treating surface of mold with fluorine-containing surface preparation agent to invest the mold with release property, a process comprising a step of carrying out the imprint with intervention of flourine-containing gas such as pentafluoropropane gas, etc. at interface between photo-curable composition and mold have generally been known. On the other hand, the improvement of adhesion to substrate has been tried through the surface preparation of substrate or the modification of composition of the photo-curable composition.
Though the adhesion to substrate and the release property from mold are conflict properties, in order to increase productivity, further improvement is required. In order to invest a material for forming coating film with these conflict properties, an addition of fluorochemical surfactant or silicone compound to the material for forming coating film has been proposed (see Patent Literature 1). However, there is still room for improvement in coexistence of the adhesion to substrate and the release property from mold.
The nanoimprint technology is a process for forming a pattern on a substrate which has, on its surface, a cured coating film to which a pattern has been transcribed with a mold (hereinafter, it is referred to also as cured film), the pattern on the substrate being formed on the basis of the pattern of the cured film. In order to form the pattern on the substrate, the substrate is subjected to dry etching with oxygen gas, fluorine-containing gas, etc. at the lean part of the cured film and the part of substrate contacting with the lean part. Since, in the dry etching, the thick part of the cured film which protects the substrate is also etched, the etching speed ratio between substrate and the cured film is important. For that reason, various photo-curable compositions which is hardly etched by said etching gas have been developed (hereinafter, this property is also called “etching resistance”).
In order to improve the etching resistance, the photo-curable composition comprising hydrolysable organic silicon compound has been proposed (see, for example, Patent Literatures 2-5). More particularly, the photo-curable composition comprising inorganic oxide particle or hydrolysable organic silicon compound has bee proposed (see Patent Literature 2). The photo-curable compositions comprising hydrolysate which is obtained by hydrolyzing hydrolysable silicon compound with water in the amount that is equal to or more than the number of moles of hydrolysable group have also been proposed (see Patent Literature 3, 4). Moreover, the photo-curable composition which comprises a compound produced by reaction between a compound having hydroxyl group and polymerizable group and a hydrolysable silicon compound has been proposed (see Patent Literature 5). Using these photo-curable compositions, it is possible to form a cured film having improved etching resistance.
However, the studies of inventors revel that even in the photo-curable compositions whose etching resistance is improved, there are rooms for improvement in the following points.
For example, since the inorganic oxide particles are used in the photo-curable composition disclosed in the Patent Literature 2, when insoluble impurities present in the photo-curable composition are removed, it is difficult to remove them by a filtration and subsequently there is a room for improvement in point of lowering productivity. There are easily left traces such as poor dispersion in the cured coating film (cured film) because of, probably, using the inorganic oxide particles, there is a room for improvement in case of forming finer pattern.
In the photo-curable compositions disclosed in the Patent Literatures 3 and 4, though it is presumed that it is caused by using plenty of water, there is a case that it is necessary to press the mold against the coating film with comparatively high pressure. In case that the mold is pressed against coating film with high pressure, the mold itself is easy to break and consequently is unsuitable for large-seized nanoimprint. Accordingly, in said photo-curable compositions, there is a room for improvement in the above-said point.
The photo-curable composition disclosed in the Patent Literature 5 has the composition in which the amount of water is reduced. Though, as being mentioned above, the photo-curable composition disclosed in the Patent Literature 5 comprises the organic silicon compound having polymerizable group, which is synthesized by an equilibrium reaction between hydroxyl group and alkoxy group, it is presumed that the reaction portion between hydroxyl group and alkoxy group is ease to be hydrolyzed again. For that reason, though it is presumed that it is caused by a fact that the dispersion state of hydrolysate of organic silicon compound (mainly inorganic component) in polymer of polymerizable monomer (mainly organic component) is deteriorated, there is a case that the filterability is lowered. There is also a case that the transcription property of pattern is poor and accordingly there is a room for improvement.